In the tape sealing of rectangular shipping cartons, a preliminary requirement involves folding of the carton front, rear and side flaps from upwardly directed positionings of each to closed lateral positions wherein the side or major flaps overlay the front and rear (minor) flaps with longitudinal edges of the folded side flaps defining a, e.g., upper carton seam, sealing tape thereafter being applied in a sealing course over this seam with anchorage lengths of the tape course being adhered to portions of the carton front and rear walls. By simplest means, the flap folding can be hand effected by a machine operator immediately prior to passing the closed contents-containing carton onto the conveyor of a taping machine. This procedure is in most cases undesirably labor intensive for continuous carton sealing operations so flap folding devices are used, these devices generally being part of the tape sealing machine or an adjunct thereto so that passage of an open flap carton through the taping operation will result automatically in operation of these flap folding devices to effect flap closure before the carton reaches a tape applying station. U.S. Pat. No. 3,382,645 discloses a form of such flap folding devices, which devices comprise, inter alia, front (minor) flap folding arm 146, obliquely downwardly extending folding plows 233 for folding the carton side (major) flaps and a rear (minor) flap folding kicker 161. Normally upwardly disposed plates which are pivoted near their bottoms also can be used to effect folding of the carton side flaps. When the front edges of these side flaps on a forwardly travelling carton engage the plates, the plates are caused to pivot and with that pivoting movement fold down and inward the carton side flaps.
While the aforementioned devices employed for side flap folding operate satisfactorily for the intended purpose, problems can be encountered in certain instances in their use. These devices operate on the basis of the front edges of the side flaps of a forwardly travelling carton coming into contact with an obstruction. i.e., a fixed or rigid folding plow or twisted folding rod, or a plate pivoted at its bottom, to initiate and carry out the side flap folding movement. Where heavy material carton structures are involved, i.e., double and triple wall corrugated material cartons, the stiffness of this material as present in the upstanding side flaps can lead to failure of the side flaps to bend or bend properly on contacting the folding devices so that due to this malfolding coupled with momentum effect in the travelling carton, there can result undesirable happenings such as a ripping of the side flaps away from their associated carton side walls or formation of a new false score in the carton structure or only partial flap folding and consequent partial flap sealing. In these prior devices, the whole reaction force of the engagement of the side flaps with the folding devices is transmitted to the side flaps. In addition to the heavy, stiff nature of carton materials, the score line provided where a side flap meets an associated carton side wall and which is intended to function as a flap folding axis may be of low quality so that the side flap will not start to fold down and inward when it engages the folding device but rather impact the device and tear or rip away from the associated side wall where it has joinder thereto.
The above-described problems also are prevalent in respect of a class of rectangular shipping cartons which are formed from corrugated paperboard stock fabricated in the Far East and manufactured from a material base which lacks a certain quality of stiffness and strength to resist tearing, e.g., paperboard made from rice and rice plant fibers.
Thus it is to be understood that flap folding devices as are known can be a problem not only with use of cartons made from paperboard stock which is too stiff or strong but also with those made from paperboard which is not stiff enough and lacks tear-resistant strength because in both situations, use of such flap folding devices frequently results in unwanted and unacceptable flap damage.